The atmosphere surrounding the Earth contains small quantities of ozone— a gas that plays a fundamental part in life on Earth. This is because ozone is able to absorb the major part of Sun’s ultraviolet radiation and therefore prevent this dangerous radiation from reaching the Earth’s surface. Without a protective ozone layer in the atmosphere, animals and plants could not exist, at least upon land. It is therefore important to understand the processes that regulate the atmosphere’s ozone content. Especially, after the discovery of a ‘hole’ in the ozone layer over Antarctica that prompted global action. Paul Crutzen of the Max-Planck-Institute for Chemistry, Germany, along with his colleagues, Sherwood Rowland and Mario J Molina, made pioneering contributions to explaining how ozone is formed and decomposes through chemical processes in the atmosphere. Most importantly, their work showed how sensitive the ozone layer is to the influence of dangerous emissions of certain compounds. By explaining the chemical mechanisms that affect the thickness of the ozone layer, the three researchers have contributed to our salvation from a global environmental problem that could have catastrophic consequences. Recognition for their work came in the form of Nobel Prize in Chemistry in 1995. On a recent visit to India, Crutzen spoke to Ashok B Sharma on the growing concern over the climate change and the need to safeguard the ozone layer. Excerpts:

How do you look at the current debate on the global climate change?

The impact on the global environment owing to hectic human activity has escalated. Because of this and also due to emissions of carbon dioxide and nitrogen, global climate may change significantly from its natural behaviour for the millennia to come. Today, we live in a period that can appropriately be called the ‘Anthropocene Period’ – a new geological epoch in which humankind has emerged as a globally significant and potentially important force capable of reshaping the destiny of the planet. This period supplements the warm Holocene Period of the past 10-12 millennia. The Anthropocene Period could be said to have started in the latter part of the 18th century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane. To assign a more specific date to the onset of the Anthropocene Period seems somewhat arbitary. Even then, we propose the latter part of the 18th century, which coincides with James Watt’s invention of the steam engine in 1784. We are aware that alternative proposals can be made – some may even want to include the entire Holocene Period.

Do you not feel serious attempts are being made through global treaties to limit the emissions of greenhouse gases? Has the Montreal Protocol proceeded well?

Public awareness has been generated and some progress has been made, but not enough. I would rather suggest a radical contingency plan as political attempts to limit greenhouse gas emissions are very pitiful. An escape route is needed if the global warming tends to run out of control. I would suggest a method of artificially cooling the global climate by releasing particles of sulphur in the upper atmosphere, which would reflect sunlight and heat back into space.

Any other remedy you would like to propose?

Around the world, attempts are being made to control the emission of carbon dioxide. Double bond hydrocarbons are reactive and hence dangerous, while single bond ones are slow in defusing. Molecular diffusion does not play any role in the atmosphere till 100 km. Bio-fuels are being produced which are, by and large, carbon neutral, but we have to see whether they are nitrogen neutral also. Nitrogenous gases are equally culprits of climate change. I have just sent my article for publication in Nature showing how dangerous nitrogenous gases could be.

More nitrogen is now fixed synthetically and applied as fertilisers in agriculture than fixed naturally in all terrestrial eco-system. The escape into the atmosphere of nitrogen dioxide from fossil fuel and biomass combustion likewise is larger than the natural inputs, giving rise to photochemical ozone (smog) formation in extensive regions of the world. We have to study the use of compressed natural gas (CNG) as auto fuels and see how much nitrogenous gases it emits.

Methane also contributes to ozone layer depletion. It is generated largely from rice fields. An alternate rice farming method should be in place that could minimise methane emission.

You were part of the team that discovered the Asian Brown Cloud (ABC) over the Indian Ocean. What could be its impact on the environment?

I was part of the United Nations sponsored project. We found the Asian Brown Cloud (ABC) over the Indian Ocean. Such brown clouds were also found over Europe in the early days of industrialisation. Asian Brown Cloud was due to pollutants and aerosols emitted in the dry season. Such clouds can inhibit solar radiation, threaten natural cycles and influence rain precipitation levels. But such clouds are a temporary phenomenon and are washed out by rain showers.

The press release issued by UNEP overstated the consequences. The scientists are, however, still studying the impact of Asian Brown Cloud. I would rather suggest India give more attention to atmospheric chemistry and find out how it impacts the monsoon rainfall. India has already suffered erratic monsoon in some years leading to drought.